This disclosure is based upon Swiss Application No. 1092/00 filed May 31, 2000, and International Application No. PCT/CH01/00293 filed May 14, 2001, the disclosures of which are incorporated herein by reference.
The present invention relates to a method and device for detecting impurities in a longitudinally moving thread-like product made of textile fibers.
A method and device for detecting contaminants, in particular foreign fibers in elongate textile structures, are known from U.S. Pat. No. 5,414,520. The structure, for example a yarn, is illuminated with light in a first sensor and the extent of the light reflected by the yarn is measured. As a result, contaminants are detected whose color, structure or surface composition differs from that of the base material of the yarn. However, deviations in the mass or diameter of the yarn can also be detected at the same time. To eliminate these deviations the structure is illuminated from the opposite side in the same or in a different sensor, so the sensor accordingly measures the shadowing owing to the structure. If the signal produced by the reflection and the signal produced by the shadowing are combined, an impurity signal is produced which is independent of the influence of the mass or the diameter of the structure. The cutting blade of a yarn clearer, or the drive of a spinning machine on which the yarn clearer is provided, is conventionally controlled by this impurity signal, to remove detected contaminants.
Every removal of a contaminant results in a cut and subsequent joining of the adjacent portions of a yarn or strip, for example by splicing. If this occurs on a bobbin winding machine, the winding head is stopped. If this occurs on a spinning machine, the relevant spinning point is stopped. This means that removal of the contaminants, for example from textile yarns, during the production process causes losses in the output of the affected machines owing to such stoppages. In particular, in spinning machines these losses consist not only of the periods of time required to separate the yarn and join it again, other stoppage times can be effected if there is an obligatory pause until the joining apparatus, which conventionally has to service many spinning points, is available and has reached the dubious spinning point. Therefore, on one hand it is desirable to remove impurities or contaminants in order to avoid problems during subsequent processing, such as weaving, dyeing or improving. However, it is not desirable for the power of the machines to be impaired thereby.
For these reasons it is desirable, for example, for the manufacturer of a textile intermediate product, such as strip, yarn etc., to be aware of whether and to what extent he wishes to remove contaminants or impurities in the strip or yarn. His possibilities for making a choice are, however, very limited if he only has the opportunity to set a threshold, beyond which a contaminant is removed or not.
It is therefore an object of the present invention to provide a method and a device with which contaminants or impurities can be detected and removed on the basis of substantially differentiated criteria.
In accordance with the invention, a first parameter is detected on a fast moving strip or yarn with a wave field, and a first signal indicating potentially present contaminants or impurities is generated. This first parameter preferably detects reflection properties that can be detected on the surface of the product. In addition, a further parameter is detected on the strip or yarn in a field, and a second signal is generated which also indicates contaminants or impurities. This second parameter preferably detects properties such as mass or diameter of the yarn or strip, which can be ascertained by measuring the shadowing of a wave field or a change in the capacitance in an electrical field. Therefore a variable, optionally belonging to a group of variables, is determined as a second parameter, this group including the mass and diameter of a portion of the product. Separate evaluation criteria, for example limit values, are allocated to the first signal and the second signal, both signals indicating possible contaminants or impurities. Finally, the evaluations of the first signal and the second signal or parameter that occur at the same location on the product are considered together, and labeled to indicate the specific type of impurity or contaminant that they represent. Thus, the type of impurity is associated with the selected evaluation criteria. Using empirical analysis, evaluation specifications can be selected to identify a group of impurities which are most likely to include a specific impurity of interest, e.g. non-vegetable contaminants.
It is particularly advantageous to ascertain the two parameters in fields which differ greatly owing to their physical properties. Therefore, very different fields can be used, for example light of different wavelengths or light and an electrical field, etc. The two parameters or the signals derived therefrom are observed or detected over a predetermined time, possibly integrated and only after this time compared with the evaluation specifications or measured with respect thereto.
The corresponding device has a first sensor operating with a wave field and a second sensor operating with a field, a processor connected to the first sensor and the second sensor with a memory for time-limited storage of the signals from the first sensor and the second sensor, and software for the processor which presets the evaluation specifications for the first and second signals. A third signal, for selecting impurities likely to include an impurity of interest, is generated from the first signal and the second signal. Light of a specific color is preferably provided for the first sensor as a wave field, and an electrical field for the second sensor.
A device for monitoring parameters of a running threadlike yarn is known from EP 0 401 600. In this device, a capacitively operating sensor and an optically operating sensor arranged adjacent to one another and provide measured values derived from the yarn. The evaluation of the two signals is not, however, made with respect to the detection of contaminants or foreign fibers, but rather with respect to the reduction in the dependence of foreign influences, such as moisture, material influence, dependence on the shape, etc., during measurement of the uniformity or for the promotion of operator-control. There is no disclosure of differentiated detection of contaminants in this publication.
A method and a device are known from GB 2,095,828 which are very similar to those from U.S. Pat. No. 5,414,520. Specifically, the reflection and transmission of light on a fiber entanglement are also measured here. The formation of the relationship of the signals from the reflection and the transmission lead to a signal allowing fibrous and vegetable faults to be distinguished. As a result of further investigations of these signals with respect to details on size, transparency to light and shape, a more precise classification of the faults may be made. This very extensive investigation of faults is, however, intended for non-wovens which are not moved quicker than about 1.5 m/min and which consist of wool, wherein those elements not originating from sheep wool are also to be regarded as contaminants. In contrast, yarns, for example, are moved during spinning at 200 to 400 m/min and during winding at up to 2,500 m/min, so in such cases these complex investigations cannot be carried out in time.
In a strip or yarn, fibers consisting of plastic material, cords, human and animal hairs, feathers etc., are referred to herein as non-vegetable contaminants or impurities, and are particularly disruptive. With cotton as the base material for the yarn, for example, leaf residue, husk portions, seed portions etc. from the cotton, which constitute vegetable contaminants or impurities, are less disruptive. In other words, vegetable contaminants are those elements originating from the cotton plant. Elements or materials not originating from the cotton plant are called non-vegetable. However, these elements can still be natural products, such as hair or feathers.
The advantages achieved by the invention can be seen in that, on one hand, the drawbacks during subsequent processing and, on the other hand, the drawbacks during production of the current intermediate product, such as the yarn or strip, can be avoided owing to a purposefully differentiated classification and elimination of selected impurities in accordance with the aforementioned points of view. As an example, a class of impurities which is most likely to contain non-vegetable impurities can be predetermined when detecting contaminants in the form of an evaluation specification for the signals received. This means, for example, that most or all of the non-vegetable contaminants could be removed, while many vegetable contaminants could be left in the yarn. Such a classification results in the advantage that many contaminants do not have to be cut out of the yarn or strip. These contaminants do not impair subsequent processing, for example dyeing, since the vegetable impurities take up the dye equally as well as the cotton. Alternatively, possible original differences in color might be compensated during bleaching. However, such a classification also results in the advantage that fewer cuts are made in the yarn and therefore the output of the spinning or bobbin winding machine is not reduced so drastically.